Analysis of experimental NRL radar altimeter data

An X-band radar designed and built by the Naval Research Laboratory and capable of continuously variable transmitted pulse durations down to 1 nsec is being flown on a NASA Wallops Flight Center C-54 aircraft to investigate the interaction of radar altimeter signals with the sea surface. There is good agreement between the observed radar altimeter leading edge rise time for a 1-nsec transmitted pulse and the rise time predicted from the radar parameters and the sea state determined by a laser profilometer. Using a threshold tracker on 29-pulse averages for a transmitted pulse of 24 nsec, we found that the range noise varied linearly with the power level of the threshold over a considerable range. The altimeter range quantization was 9.35 cm and a minimum range noise of 3.9 cm was obtained. A comparison of pulse-to-pulse correlation observed in the radar data with that predicted by a Monte Carlo simulation is used to obtain a measure of sea surface scatterer motion.